The 18-year-old will be part of Roberto Martinez's squad this season after a complicated series of manoeuvres on deadline day.

Henen had looked likely to move to Goodison Park on a permanent deal from Belgian side Anderlecht after spending preseason training at Everton's Finch Farm base.

But the Belgium youth international instead signed for Greek champions Olympiakos -- who then immediately loaned him to Everton.

The paperwork for Henen's loan move to Goodison Park was not completed until late on Monday night.

He will spend the season with Everton's under-21 side, who he will link up after playing for Belgium's under-19 side in matches against Israel and Hungary during this week's international break.

Martinez told Everton's official website: "As we had said previously, he's someone whose potential we recognise and at this stage he will go into the under-21 development squad. We are looking forward to working with him this season."

Luxembourg-born Henen joined the youth setup at Standard Liege when he was 12, then moved to Belgian rivals Anderlecht three years later.

The forward -- who was linked with a move to Manchester United when he was just 15 -- spent last season on loan at Monaco, where he played for their reserve side in the Championnat de France Amateur, the fourth tier of French football.